Our overall aim is to apply solid state NMR to oriented collagen fibrils, nature's most abundant protein, and more generally develop the technique for studying fibrous structures. We propose to use solid state 2H and 13C NMR spectroscopy of oriented collagen fibrils to directly determine essential elements of this important protein's secondary that have eluded accurate determination by x-ray diffraction. These studies make use of a special NMR fiber probe. The structural features to be determined are (i) the average orientation of individual peptide planes of the collagen tripeptide repeat relative to the fiber axis, (ii) the width of the distribution of static orientations about the average orientation and (iii) the amplitude, rate and stereochemistry of dynamic disorder in the collagen backbone. Furthermore, these properties will be determined as a function of fibril extension, temperature and hydration. 2H NMR techniques will also be used to directly examine water ordering and structure in collagen. Previously, water has been proposed as an essential feature needed for stabilizing the putative structure of the collagen triple helix but its presence has not been convincingly demonstrated. Collagen provides the proteinaceous matrix for bone, it is the dominant material in and responsible for the tensile strength of tendons and it maintains the structural integrity of veins and arteries. In more than 90% of the cases of children with the heritable disorder of osteogenesis imperfecta, there is a mutation in the genes for type I procollagen. Clinical symptoms include extreme bone fragility, hypermobility and congenital dislocation of joints, osteoarthritis, osteoporosis and skin abnormalities. The architecture of the supramolecular collagen assembly is particularly sensitive to mutations which disrupt the structure of the collagen molecule anywhere along its 3000 angstroms length, thus the collagen molecular structure is fundamental. However, refinement of the molecular structure of collagen has not progressed substantially beyond proposals given in the time span of 1976-1979, during which Prockop wrote, ".... although molecular models for collagen..... have now been refined to a considerable degree, the x-ray data have not in themselves provided a unique solution to the structure of collagen. Therefore the molecular models, without supporting kinetic and thermodynamic data, are difficult to use as the sole criteria for determining the contributions of specific amino acid residues to helical stability".